Presumptive evidence for viral cause of multiple sclerosis (MS) in man part comes from the fact some viruses are able to persist in the central nervous system (CNS) of animal hosts, thereby producing a chronic, inflammatory demyelinating disorder. Of the few available experimental animal models of virus-induced demyelination, Theiler's murine encephalomyelitis virus (TMEV) infection in mice is possibly the most relevant to human MS. The TMEV are naturally occurring enteric pathogens of mice, constituting a separate serological group within the picornavirus family, which have recently been classified as Cardioviruses. The close similarity to MS is because: (1) chronic pathological changes are virtually limited to the CNS while matter, (2) myelin breakdown leads to clinical disease, e.g. gait spasticity and weakness, and a neurogenic urinary bladder, (3) demyelination is immune-mediated, (4) susceptibility is under multigenic control with one gene mapping within the H-2D region of the major histocompatibility complex (MHC), and (5) disease susceptibility correlates with the temporal development of chronically, high levels of class Il- restricted TMEV-specific delayed type hypersensitivity (DTH). The goal of the proposed research is to elucidate molecular pathogenesis of TMEV-induced demyelinating disease in mice. The recent atomic resolution of the 3-dimensional structure of the closely related Mengovirus should greatly facilitate attempts to define B and T cell epitopes on the Theiler's virion. Therefore, we propose to carry the studies of the host's humoral and cellular immune responses to TMEV,initiated in the prior granting period, to a more molecular level. Since failure of viral clearance resulting in virus persistence is central to the evolution of demyelinating disease,it is especially important to understand how TMEV is neutralized. This will be approached by mapping neutralizing immunogenic sites (nIMs) by sequencing the RNAs of neutralizing escape mutants to neutralizing monoclonal antibodies (nMABs): determining if the mechanisms different nIMs employ in neutralization are the same: and determining il there are dominant nlMs for viral clearance and protection in vivo. Since class Il- restricted TMEV specific DTH correlates with the temporal onset of myelin breakdown and disease incidence,it will be important to map the locations out the T cell epitopes in the Theiler's coat proteins and investigate their pathogenetic role in disease production. Finally, we propose to determine the sites of TMEV persistence in the mouse CNS using in situ nucleic acid hybridization with defined probes and immunohistochemical staining.